The present invention relates to drum brakes for motor vehicles and more particularly to an automatically adjustable spacer for such a brake.
There are various known systems making it possible for the distance between the ends, moved by means of the brake motor, of two shoes fitted with friction elements of a drum brake to be lengthened automatically as a function of the wear of these.
U.S. Pat. No. 4,217,973 describes, for example, a system with a spacer of fixed length and with a lever articulated on one of the shoes. Such a system, although functioning perfectly well, has a disadvantage as regards the maintenance of the brake; in fact, the articulated lever has to be changed at the same time as the corresponding shoe in the event that the latter undergoes wear.
U.S. Pat. No. 4,503,949 describes a system with a spacer of variable length, possessing a screw/nut assembly controlled by a pawl exerting stress on a toothing. Such a system likewise functions perfectly well, but has the disadvantage of being costly.
The document GB-1,405,094 also describes a system with a spacer of variable length, but having an angle lever which is moved angularly and one of the arms of which interacts with a toothed element of another part of the spacer. Such a system has the serious disadvantage of considerable bulk because of the presence of this angle lever.
It is known that motor vehicle manufacturers would like to use drum brakes with a reliable but inexpensive automatic adjustment which does not occupy a large amount of space, so that the speed sensor required for the functioning of the wheel antilock devices can be arranged in the brake.